SEXUAL SELECTION' 



395 



colors, and having a very elegant appearance under the 

 microscope. In some cases, as with Typhosus, minute, 

 bristly, or scale-like prominences, with which the whole 

 surrounding surface is covered in approximately parallel 

 lines, could be traced passing into the ribs of the rasp. 

 The transition takes place by their becoming confluent 

 and straight, and at the same time more prominent and 

 smooth. A hard ridge on an adjoining part of the body 

 serves as the scraper for the rasp, but this scraper in some 

 cases has been specially modified for the purpose. It is 

 rapidly moved across the rasp, or, conversely, the rasp 

 across the scraper. 



These organs are situated in widely different positions. 



FlO. 25.— Necrophorus (from Landois). r. The two rasps. Left-hand figure, part of 

 the rasp highly magnified. 



In the carrion-beetles (ISTecrophorus) two parallel rasps 

 (r, Fig. 25) stand on the dorsal surface of the fifth abdom- 

 inal segment, each rasp" consisting of 126 to 140 fine 

 ribs. These ribs are scraped against the posterior margins 

 of the elytra, a small portion of which projects beyond the 

 general outline. In many Grioceridae, and in Glythra 4- 

 punctata (one of the Chrysomelidse), and in some Tene- 

 brionidse, etc.," the rasp is seated on the dorsal apex of the 



" Landois, "Zeitsolirift fur Wiss. Zoolog.," B. xvii., 1867, s. 227. 



'* I am greatly indebted to Mr. G. R. Crolcli for liaving sent me many pre- 

 pared specimens of various beetles belonging to these three families and to 

 others, as well as for valuable information. He believes that the power of 

 Stridulation in the Olythra has not been previously observed. I am also much 

 indebted to Mr. E. W. Janson, for information and specimens. I may add that 

 my son, Mr. F. Darwin, finds that Dermesies tnurinus stridulates, but he 

 searched in vain for the apparatus. Scolytus has lately been described by 

 Dr. Chapman as a stridulator, in the "Entomologist's Monthly Magazine," 

 vol. vi. p. 130. 



